Journal
PSYCHOPHARMACOLOGY
Volume 195, Issue 1, Pages 71-84Publisher
SPRINGER
DOI: 10.1007/s00213-007-0882-0
Keywords
quinolinic acid; excitotoxin; lesion; nucleus accumbens; inter-temporal choice; delay of reinforcement; delay discounting; rat
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Rationale There is evidence that lesions of the nucleus accumbens core (AcbC) promote preference for smaller earlier reinforcers over larger delayed reinforcers in inter-temporal choice paradigms. It is not known whether this reflects an effect of the lesion on the rate of delay discounting, on sensitivity to reinforcer magnitude, or both. Aim We examined the effect of AcbC lesions on inter-temporal choice using a quantitative method that allows effects on delay discounting to be distinguished from effects on sensitivity to reinforcer size. Materials and methods Sixteen rats received bilateral quinolinic acid-induced lesions of the AcbC; 14 received sham lesions. They were trained under a discrete-trials progressive delay schedule to press two levers (A and B) for a sucrose solution. Responses on A delivered 50 mu l of the solution after a delay d(A); responses on B delivered 100 mu l after d(B). d(B) increased across blocks of trials, while d(A) was manipulated across phases of the experiment. Indifference delay d(B(50)) (value of d(B) corresponding to 50% choice of B) was estimated in each phase, and linear indifference functions (d(B(50)) vs d(A)) derived. Results d(B(50)) increased linearly with d(A) (r(2) > 0.95 in each group). The intercept of the indifference function was lower in the lesioned than the sham-lesioned group; slope did not differ between groups. The lesioned rats had extensive neuronal loss in the AcbC. Conclusions The results confirm that lesions of the AcbC promote preference for smaller, earlier reinforcers and suggest that this reflects an effect of the lesion on the rate of delay discounting.
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